Lagrangian dynamics in inhomogeneous and thermal environments, An application of the Onsager-Machlup theory I

Alexander Jurisch

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arXiv · 2012.06820

Lagrangian dynamics in inhomogeneous and thermal environments, An application of the Onsager-Machlup theory I

Alexander Jurisch

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Abstract

We straight-forwardly derive the Onsager-Machlup Lagrangian from the Fokker-Planck equation and show that friction and dissipation are a natural property of the equation of motion. We develop a method to calculate the local variance $\sigma_{2}\,b(q)^{2}$ and identify this function as a Helmholtz-factor. In both meanings the function $b(q)$ describes properties of the environment. For application, we examine the free fall through a barometric medium and model a blow of wind by a solitonic pulse running through the medium. We treat harmonic oscillators immersed in a thermal bath, finding intuitive as well as counter-intuitive phenomena of friction. By allowing the temperature to be time-dependent, the dynamical process of cooling and heating becomes self-consistently available. We find a state of dynamical balance between system and environment. Last, we show that dynamical balance is related to adiabatic thermodynamic processes. In a special case, dynamical balance can induce a real phase-transition.

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Alexander Jurisch. 2020-12-12. Lagrangian dynamics in inhomogeneous and thermal environments, An application of the Onsager-Machlup theory I. https://arxiv.org/abs/2012.06820

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